Semiconductor devices often include multiple layers of conductive, insulating, and semiconductive layers. Often, the desirable properties of such layers improve with the crystallinity of the layer. For example, the electron mobility and electron lifetime of semiconductive layers improve as the crystallinity of the layer increases. Similarly, the free electron concentration of conductive layers and the electron charge displacement and electron energy recoverability of insulative or dielectric films improve as the crystallinity of these layers increases.
For many years, attempts have been made to grow various monolithic thin films on a foreign substrate such as silicon (Si). To achieve optimal characteristics of the various monolithic layers, however, a monocrystalline film of high crystalline quality is desired. Attempts have been made, for example, to grow various monocrystalline layers on a substrate such as germanium, silicon, and various insulators. These attempts have generally been unsuccessful because lattice mismatches between the host crystal and the grown crystal have caused the resulting layer of monocrystalline material to be of low crystalline quality.
If a large area thin film of high quality monocrystalline material were available at low cost, a variety of semiconductor devices could advantageously be fabricated in or using that film at a low cost compared to the cost of fabricating such devices beginning with a bulk wafer of semiconductor material or in an epitaxial film of such material on a bulk wafer of semiconductor material. In addition, if a thin film of high quality monocrystalline material could be realized beginning with a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the high quality monocrystalline material.
Some functions related to microresonators have been unavailable or limited in current technologies because of the unavailability of a low cost wafer structure that includes high quality compound monocrystalline materials in thin layers over a silicon substrate. Existing microresonators include non-gained controlled resonators including those whose critical coupling is controlled by tuning the resonant wavelength by varying the effective index of refraction either through temperature control or by varying the refractive index of a material in the evanescent field region immediately surrounding the resonator (e.g. in an electro-optic polymer material). Another implementation of a gain-controlled resonator uses an optically emitting doped oxide material overlying the resonator that is photo-pumped.